The present invention relates generally to the art of welding power supplies. More specifically, it relates to inverter welding power supplies driven by an engine.
There are different types of prior art welding power supplies. Two types of welding power supplies are phase controlled and inverter-based power supplies. Both types typically receive an ac line (60 Hz) input. However, inverter power supplies can be controlled to a desired frequency, but phase controlled power supplies are limited to the input frequency. Also, phase controlled power supplies cannot be used for pulse spray processes. Inverter-based power supplies are often preferred because they are lighter, have a faster response, provide better weld characteristics, and are better suited for multiple processes (MIG, TIG, stick etc.).
An inverter power supply receives a dc input (often called the dc bus), and switches the input to provide an ac output. Prior art inverter welding power supplies have been designed to receive a line frequency input (60 or 50 Hz), and to rectify that input to produce the dc bus.
The inverted ac output can be used as the welding output. However, some prior art welding power supplies include a rectifier which rectifies the ac inverter output to provide a dc welding output. The dc input to the inverter is typically obtained by rectifying an ac line input. Many inverter power supplies have controls which allow the power supply to effectively convert the ac line power into useful dc (and sometimes ac) welding power.
Engine driven generators used in welding are also common. An engine driven welding power supply is necessary for applications where the user needs to weld at multiple locations and finds it necessary to move the welding power supply. An auxiliary power output (110 or 220 VAC) is usually provided for power tools, lights etc. Typically, engine driven generators are used to drive a simple tapped reactor or phase controlled power supplies. They often require an engine and generator specifically designed for the welding power supply, which can be more expensive than using a standard engine/generator. Phase controlled engine drive welding power supplies necessarily include all of the disadvantages of phase controlled power supplies.
Another prior art engine driven welding power supply is a dc welding power supply, wherein the dc output of the generator is used directly for a dc welding output. Such a welding power supply, with field control, is shown in U.S. Pat. No. 4,465,920, issued to Hoyt et al.
A few prior art inverter welding power supplies have been connected to a generator output and used as engine driven inverter welding power supplies. The generator ac output serves as the ac inverter input (which is rectified to create the dc bus). This arrangement creates many problems. First, inverter based welding power supplies have heretofore been designed to receive the relatively stable and constant ac line voltages A generator does not always produce such a stable and constant output. Second, there has not been an integrated control system wherein the engine and or generator is controlled in response to the welding output or inverter operating parameters. Thus, these engines usually operate at full throttle constantly, and are very inefficient.
The common practice of providing an auxiliary power output on the generator has at least one disadvantage. The auxiliary power is single phase, 120 or 240 VAC at 50 or 60 Hz, and is used for power tools, lights etc. However, the single phase output unbalances the three phase output, and the result is harmonic distortion in all three phases. The distortion will cause one of the phases to have much higher peak voltage than the other two phases. The unusually high peak voltage may damage the inverter input capacitors, or require larger capacitors.
The distortion is caused by a backward component of a magnetic field wave. When a three phase load is present the three stator currents produce a magnetic field wave that rotates in the same direction as, and at the same speed as, the rotor. Thus, there is no relative motion between the rotor and the magnetic field wave, and the magnetic field wave does not induce any voltage in the rotor. However, when the load is unbalance the magnetic field wave created by the stator currents does not move at the speed as and in the same direction as the rotor. The magnetic field produced by the stator currents when an unbalanced load is present may be resolved into two components: a forward component that is in the same direction and at the same speed as the rotor, and a backward component. The forward component behaves as a balanced three phase load, and does not cause a problem. The backward component is moving at the same speed as the rotor, but in the opposite direction. Thus, it has a motion relative to the rotor of twice the generator speed. This xe2x80x9cmovingxe2x80x9d magnetic field will induce voltage in the rotor field winding, which causes the high output voltage. Damper cages have been used in generators (although not necessarily in the welding art) to counter-act or compensate for the effect of unbalanced loads.
Accordingly, it would be beneficial to have an inverter-based welding power supply that is engine driven where the control is integrated to control the engine and generator in response to either welding or inverter operating parameters. Preferably the generator will counter-act or compensate for the effect of unbalanced loads. Also, the power supply will preferably be able to be used for pulse spray and other welding processes.
According to a first aspect of the invention a method for providing welding power includes generating an electrical output with an engine and an ac or dc generator. The output is rectified if needed, and inverted to provide an ac inverter output. The engine is controlled using feedback indicative of a welding output operating parameter.
Another aspect of the invention is controlling engine speed in response to the feedback. Also, the speed may be specifically controlled to select between an idle speed and a run speed in response to the feedback. Other aspects include controlling one or more of a throttle position, a fuel pump, an injection timer, a fuel to air ratio, fuel consumption and ignition timing.
Another aspect of the invention is having the feedback be responsive to one or more of the welding current, welding voltage, welding power, or functions thereof.
Another aspect of the invention is obtaining a signal responsive to the output power and a function thereof by multiplying signals representative of the voltage and current to obtain a signal representative of the power, and then integrating the signal representative of the power.
Yet another aspect of the invention includes the step of storing energy after rectifying, and controlling the engine by increasing engine speed when the energy stored decreases past a threshold.
One alternative aspect of the invention is having the feedback be responsive to ripple in the output. Another alternative aspect includes the step of rectifying the inverter output to provide a dc welding output.
Another aspect of the invention is a stand alone welding power supply that includes a primary mover mechanically coupled to a rotating shaft. A generator includes a rotor mechanically coupled to the shaft and the generator also includes a stator magnetically coupled to the rotor. Thus, the generator provides an ac output. An inverter is connected to the ac output through a rectifier and the inverter inverts power from the ac input to provide an inverted output. A controller is coupled to the engine and has a feedback input connected to a feedback circuit. The feedback circuit is also coupled to the welding output, and a signal responsive to at least one welding output operating parameter is provided to the feedback input. A do generator, without subsequent rectification, is used in another embodiment.
Yet another aspect of the invention includes a speed control for the primary mover and the controller includes an output coupled to the speed control, wherein the speed of the primary mover is controlled in response to the feedback signal. One embodiment provides for selecting between an idle and run speed in response to the feedback signal. Alternatives include controlling one or more of a throttle position, a fuel pump, an injection timer, a fuel to air ratio, fuel consumption and ignition timing.
Other aspects of the invention include deriving the feedback from welding current, welding voltage, welding power, ripple current, ripple power, ripple voltage and/or functions thereof. The power and a function thereof may be obtained from a circuit that multiplies signals representative of voltage and current to obtain a signal representative of power, and a circuit that integrates the signal representative of power.
Yet another aspect of the invention includes one or more input energy storage device that stores energy after rectification and wherein the controller causes the engine to increase speed when the energy stored decreases past a threshold.
Another aspect includes a rectifier coupled to the inverter output to provide a dc welding output.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.